How to get classes in a Source Generator that implement say an Interface in the Target Project

I'm attempting to write a set of source generators to generate factory classes in a Blazor application.

The older examples all use ISourceGenerator which I believe has been superceded byIIncrementalGenerator.

The only good example I can find is the EnumGenerator (goes into any detail beyond the many posts that regurgitate the same trite and useless examples).

What I want is find all the classes that implement an interface, pull some information from them (maybe a class based attribute if I can't extract it any other way) and then generate a factory class. Old examples use context.Compilation.SyntaxTrees, but that approach is now outdated.

Here's some sample code:

[Generator]public class MySourceGenerator : IIncrementalGenerator{    public readonly record struct PresentationFactoryToGenerate    {        public readonly string Name;        public readonly string Id;        public readonly string Editor;        public PresentationFactoryToGenerate(string name, string editor, string id)        {            this.Name = name;            this.Editor = editor;            this.Id = id;        }    }    public void Initialize(IncrementalGeneratorInitializationContext context)    {        Debugger.Launch();        var presenters = Enumerable.Empty<PresentationFactoryToGenerate>();        // STUCK HERE        // Get the list of presenters implementing IEditPresenter        foreach (var presenter in presenters)            context.RegisterPostInitializationOutput(ctx => ctx.AddSource($"{presenter.Name}EditPresenterFactory.g", SourceText.From(BuildPresenterFactory(presenter), Encoding.UTF8)));    }    private string BuildPresenterFactory(PresentationFactoryToGenerate item)    {        var code = $$"""                namespace Blazr.App.Presentation;                public class {{item.Name}}EditPresenterFactory                {                    private readonly IServiceProvider _serviceProvider;                    public {{item.Name}}EditPresenterFactory(IServiceProvider serviceProvider)                    {                        _serviceProvider = serviceProvider;                    }                    public async ValueTask<IEditPresenter<{{item.Editor}}, {{item.Id}}}>> GetPresenterAsync({{item.Id}} id)                    {                        var presenter = ActivatorUtilities.CreateInstance<FarmEditPresenter>(_serviceProvider);                        ArgumentNullException.ThrowIfNull(presenter);                        await presenter.LoadAsync(id);                        return presenter;                    }                }""";        return code;    }}